Nitrogen Dioxide
- Sources
- Impacts
- Testing
Sources
Sources of Nitrogen Dioxide (NO2)
Nitrous Dioxide (NO2) is a reddish-brown gas with a pungent, bitter smell, which is predominantly produced during the combustion of fossil fuels. NO2 levels are typically higher in major urban areas due to emissions from car exhausts in densely populated areas, which in turn can affect indoor air quality.
Some sources of indoor NO2 emissions include tobacco smoke, combustion appliances (e.g., stoves, boilers, ovens, heaters), and fireplaces. People may also come into contact with high concentrations of NO2 in locations such as silage solos or underground car parks.
It's important to note that NO2 is commonly discussed alongside Nitric oxide (NO) using the umbrella term NOx, meaning any type of Nitrogen oxides. The term is used because NO, which is also produced during fossil fuel combustion, can quickly react with other compounds, such as O3, to form NO2. NO2 can also react under sunlight to form O3 (Ozone), which can cause extensive damage to human health.
Air Quality Management Areas (AQMAs) are designated areas within the UK which have failed to reduce air pollution to below legislative limits. Although this can apply to any pollutant, in the UK, this has overwhelmingly been applied for breaches in NO2 limits, as specified in the Air Quality Standards Regulations (2010).
There are 371 AQMAs related to NO2, which is significantly higher than the 20 AQMAs related to PM10. With such high rates of traffic, the majority of London is essentially designated as an AQMA.
It's easy to see if you are within an AQMA by using DEFRA's interactive map found on their official .GOV website.
DEFRA was successfully sued 3 times by NGO organisation ClientEarth between 2014-2020 due to its poor practice in combating levels of NO2 by issuing inadequate action plans (in relation to the Air Quality Standards Regulations, 2010) to local authorities.
Typical Sources of NO2
- Roadside Traffic
- Combustion of Fossil Fuels
- Tobacco Smoke
- Domestic Combustion Appliances
Impacts
Impacts of Nitrogen Dioxide (NO2)
Short-term exposure to NO2 concentrations higher than 200 µg/m3 can cause inflammation of the airways, which can exacerbate chronic respiratory and cardiovascular diseases, and increase the likelihood of developing respiratory infections. Long-term NO2 exposure can lead to the development of asthma in children, damage lung tissue, and reduce immunity to lung infections such as bronchitis. Reduced lung function and lung damage from extended NO2 exposure increase the likelihood of hospital visits, so it's important to keep NO2 within safe levels to avoid respiratory and cardiovascular health risks.
Common Impacts of NO2
- Inflammation of the Airways
- Development and Exacerbation of Asthma
- Increased Emergency Department and Hospital Admissions
- Increased Risk To Respiratory Infections
Testing
Testing for Nitrogen Dioxide
A range of tests is available for detecting Nitrogen Dioxide. While longitudinal sampling is effective at measuring NO2 levels, point-in-time readings of NO2 can be low in validity due to its residence time being very short in urban environments, being converted to NO, then back again in very short time frames. Similar to TENAX tubes for TVOCs, NO2 uses an acrylic tube with the absorbent triethanolamine. Concentrations of NO2 can be inferred from the level of nitrite ions attracted to the absorbent.- Acrylic Diffusion Tubes
- Passive Longitudinal Sampling
There are no legislative limits to NO2 levels in the UK, so we must refer to and infer from outdoor NO2 limits instead. NO2 must not exceed concentrations of 40 µg/m3 on average per annum in outdoor air. UK WELs set NO2 exposure at 960 µg/m3 over an 8-hour period. The 2021 WHO air quality guidelines state NO2 must be under 25 µg/m3 for a 24-hour limit.
- Air Quality Standards Regulation (2010); Annual mean concentration of NO2 must not exceed 40 µg/m3
- UK WELs: Not exceed 960 µg/m3 over an 8-hour period
- WHO 2021 Air Quality Guidelines: Less than 25 µg/m3 average over a 24-hour period
Nitrogen Dioxide FAQs
Why Is NO2 Sometimes Called NOx? ↓
Nitrous Dioxide (NO2) is often referred to using the umbrella term Nitric Oxides (NOx) because NO and NO2 are typically found in the same environment. Due to their ability to react with each other, accurately measuring the levels of NO would be impossible, as many NO compounds would have already turned into NO2 by the time you begin counting. Because the presence of one of these compounds indicates the presence of the other, we typically refer to NOx instead of NO or NO2.
Can I Perceive NO2? ↓
Yes, in high quantities, we can perceive NO2 with its harsh, pungent odour. NO2 is particularly noticeable in areas of busy traffic, especially with stop-start traffic, because NO2 is produced more readily in an idle engine. If you're ever in an area with a high volume of cars within a small area, you're more likely to notice NO2 through its smell.
Can NO2 Come From Indoor Sources? ↓
What UK Legislation Refers To NO2? ↓
Air Quality Standards Regulation (2010); EH40/2005.
How Do I Remove NO2 From My Indoor Air? ↓
Do not smoke indoors. Ensure effective filtering of outdoor air into indoor spaces, as NO2 will mainly come from automobile combustion in busy urban environments or areas with high congestion.
Why Choose ARM?
ARM offers expert NO₂ monitoring and mitigation, especially in urban environments. Our passive and real-time testing methods deliver actionable insights.
We are SafeContractor certified, a member of BESA, and our CEO Adam Taylor chairs the BESA Indoor Air Quality Group. This ensures our advice is grounded in the latest health data and guidance, giving you peace of mind and regulatory confidence.
